Overall, organic foods are not nutritionally superior to conventional foods, neither are they safer regarding bacterial contamination, researchers from Stanford University School of Medicine reported in Annals of Internal Medicine. The scientists emphasized that they did not find any significant evidence pointing to nutritional benefits linked to the consumption of organic foods. They did, however, find “weak evidence” of higher phenol levels in organic produce.

While eating organic vegetables and fruits does mean that the consumer has approximately 30% less exposure to pesticide residues, conventional foods are well below threshold limits set by regulatory authorities anyway, the authors explained.

Crystal Smith-Spangler, MD, MS, Dena Bravata, MD, MS, and team carried out a review of 17 human studies and 223 other studies of nutrient and contaminant levels in fresh foods, including pork, beef, chicken, eggs, milk, grains, vegetables and fruit. Their aim was to compare the safety, nutritional and health characteristics of conventional and organic foods.

Dr. Bravata, after carrying out a literature search, found that most of the studies were “confusing”. Some of the ones that appeared in trade publications were not very thorough. There seemed to be no study with a comprehensive synthesis of evidence which clearly showed the benefits versus the harms of conventional and organic foods.

Studies on organic foods have produced varying results. One in February 2012 found that organic rice may have high levels of arsenic.

A 2010 study published in PLoS ONE reported that organic strawberries have more antioxidants and vitamin C but less potassium and phosphorus than conventionally grown strawberries.

The research team found no compelling evidence in any of the studies that they reviewed which demonstrated that organic foods are considerably more nutritious than other foods.

Dr. Smith-Spangler said, “some believe that organic food is always healthier and more nutritious. My colleagues and I were a little surprised that we didn’t find that.”

There was some weak evidence showing that organic foods have much higher levels of phenols, which are said to be strong antioxidants, than conventional foods. There was also some evidence that omega-3 fatty acid levels in organic milk are higher. However, as deficiency in these compounds is fairly rare anyway; the authors believe these findings have “little clinical significance”.

The scientists found that organic foods had higher levels of nitrogen than other foods. They believe this is likely to be because of different uses of fertilizers. Another factor might be that organic foods are harvested at different stages of ripeness. They added that a higher nitrogen content “is unlikely to provide any health benefits”.

In 1997, sales of organic foods were worth $3.6 billion in the USA; this rose to more than $26 billion in 2010.

US consumers typically have to pay much more for organic foods, sometimes twice as much, compared to conventional food prices.

Organic foods are produced using farming methods which do not involve applying pesticides or chemical fertilizers, they are not processed using industrial solvents, chemical food additives, or irradiation.

Organic foods of animal origin, such as dairy goods and meats, come from animals that are usually free range (they roam outdoors), the authors explained. In some countries, however, free range and organic are completely different terms – free range might not necessarily mean organic, while non-free-range animals may be fed organic foods and produce organic milk and meats.

Dr. Smith-Spangler said:

“There are many reasons why consumers may choose to purchase organic food. We examined published literature to assess the evidence for significant differences in nutrition, food safety, and health outcomes between organic and conventional foods and populations consuming these foods. However, consumers may choose to purchase organic foods for other reasons besides nutrition and food safety, such as concern for animal welfare, the environment, or preferences in taste.”

The scientists stressed that there were no health studies which concentrated on the long-term health outcomes of people who consumed organic foods versus conventional foods. Of the over 200 reports they assessed, the time-spans ranged from two days to a maximum of 24 months. Put simply, we still have no idea whether organic foods are better than conventional foods over the long term.

A 2009 study funded by the Food Standards Agency, UK, and carried out by scientists from the London School of Hygiene and Tropical Medicine, found that organically produced foods are no better than conventionally produced foods, from a nutritional point of view.

Researchers from the University of California reported in the Journal of Agricultural Food Chemistry that organically grown tomatoes have considerably higher levels of flavonoids than non-organic ones. Their study had lasted ten years. They concluded that organic tomatoes are better for heart health and controlling blood pressure.

Most scientists agree that intensive livestock farming has contributed to the rapid spread of antibiotic-resistant bacteria. A team of scientists from the University of Maryland School of Public Health found that organic farming helps reduce the threat of antibiotic-resistant bacteria.

The Soil Association, a UK charity that campaigns for healthy, humane and sustainable food, farming and land use, welcomed some aspects of the study findings while criticizing others.

Describing this American study of “limited application in Europe”, the Association said it is glad to see that it recommends organic food as a way of avoiding pesticides, because this is the main reason most people opt for organic foods.

The Soil Association welcomed the report’s description of organic milk as being significantly more nutritious that conventional milk, as well as the higher likelihood of non-organic chicken and pork containing antibiotic-resistant bacteria.

In a communiqué, the Soil Association wrote:

“Unsurprisingly, perhaps, the focus is placed on highly contestable negatives over incontrovertible positives, such as reduced chemical use, exclusion of controversial additives such as aspartame and MSG, higher animal welfare and increased biodiversity, to name a few.”

The charity says the study’s methodology was flawed. The research team failed to include any studies which were not written in English, and only chose to look at some selected ones which were in the English language.

It says that while the Stanford University team’s methodology might be suitable for comparing different medication trials, it cannot simply be applied to assessing various crops. A medication used in one part of the world will typically behave identically in another part; this is not the case with, for example, potatoes grown in different climates and soils.

The Soil Association wrote:

“Studies that treat crop trials as if they were clinical trials of medicines, like this one, exaggerate the variation between studies, and drown out the real differences. A UK review paper, using the correct statistical analysis, has found that most of the differences in nutrient levels between organic and non-organic fruit and vegetables seen in this US study are actually highly significant.”

Written by Christian Nordqvist